Sen. Al Franken, D-Minn., returned $40,822 donated to him from a Boston law firm currently being investigated for potentially illegal campaign contributions.

An investigation into the Boston-based Thorton Law Firm by The Boston Globe and the Center for Responsive Politics revealed that Thorton essentially reimbursed employees for political contributions through bonus checks that totaled the exact amount of the donation.

This type of action is on dicey legal grounds as it hides the true identity of the person donating behind multiple names. This behavior from the Thorton Law Firm also has implications regarding state campaign finance law. In Massachusetts, it is illegal for corporations and partnerships to donate money directly to political candidates.

Franken isn’t the only politician to have to hand over funds. Then-Senate candidates Tammy Duckworth from Illinois and Maggie Hassan from New Hampshire had to return $26,100 and $51,000, respectively. Former presidential candidate Hillary Clinton gave back $20,000 from the embattled firm.